Composite structure comprising a component of electro-cast refractory and elements highly resistant to corrosion and erosion

ABSTRACT

A composite and monolithic refractory structure, particularly adapted for making furnaces for glassmaking or the like, constituted by a block-shaped component made of electro-cast refractory material based on oxides of aluminum, zirconium, silicon, and the like, having shapes and dimensions that are adapted for its uses, inside which at least one protective element is monolithically inserted; the protective element is highly resistant to the attack of molten glass baths or the like and is chosen among metals, noble metals, refractory metals, refractory materials, conventional and non-conventional ceramic materials, such as carbides, nitrides, borides, and the like, or graphite-based materials, alloys and/or compounds and/or composites thereof; the element is provided substantially in the shape of a plate that is shaped and sized so as to have a profile that is similar to the peripheral profile of the refractory block and is arranged, inside the block, so that its surfaces are located at, and proximate to, the surfaces of the block that are meant to be exposed to the attack of the bath, so as to constitute an insert that acts as a continuous protective barrier against the attack for the refractory component. The scope of the invention also includes a process for producing the composite refractory structure in conventional molds.

BACKGROUND OF THE INVENTION

The present invention relates to a composite refractory structureconstituted by an electro-cast refractory component based on ceramicoxides, refractories and other materials, and mineral oxides, whichincludes at least one variously shaped structural element that is highlyresistant to corrosion and/or erosion produced by molten baths and inparticular by baths of molten glass and the like.

The scope of the present invention also includes a process for producingsaid monolithic composite refractory structure, which can be used tomake furnaces for glassmaking and particularly in the regions of thefurnace that are most intensely subjected to the corrosive action ofmolten glass.

It is known that the technology for building glassmaking furnaces usesappropriately assembled monolithic elements made of electro-castrefractory material which are usually termed "electro-cast blocks".

These electro-cast blocks are produced in various shapes, sizes, kinds,and qualities, and are all obtained by casting a mixture of moltenrefractory oxides in a three-phase electric-arc furnace, as disclosed inItalian patent Application 19461 A/87 of Feb. 23, 1987.

The molten mixture is cast into appropriately designed and shaped molds,where it undergoes a first partial cooling and assumes the intendedshape. The electro-cast refractory material then completes its coolingcycle in controlled conditions; at the end of this cycle, it is usuallymachined and finished mechanically.

This final product is commonly termed "electro-cast refractory block".

It is also known that the electro-cast refractory material is attackedduring use, as a consequence of the various mechanical, physical, andchemical conditions that occur in each part of the furnace.

The attack to which the electro-cast refractory is subjected wears itaway. The extent of the wear determines the duty life of the blocks ofelectro-cast material and substantially determines the duty life of theglass furnace.

The wear of blocks of electro-cast material is different according totheir quality, type, and location in the furnace. In fact, it is knownthat there are areas in the furnace where wear is more intense than inothers. It is widely acknowledged that among the most intense wear whichoccurs, there is the wear in the electro-cast blocks that compose thethroat of the furnace, in particular the throat cover block at the glassinlet, the weir wall, or in the area of the blocks that is technicallydefined as "flux line" or "metal line".

In order to extend the life of a glass furnace as much as possible, goodpractice selects and assembles together electro-cast refractories havingdifferent qualities and properties in order to balance the extent ofwear in every part of the furnace.

In the production of glass furnaces it is in fact now common tosimultaneously have blocks of electro-cast refractory having differentchemical compositions (Al₂ O₃ --ZrO₂ --SiO₂, alpha and beta Al₂ O₂,ZrO₂, Al₂ O₂ --Cr₂ O₃ --SiO₂ --ZrO₂, etcetera), located in specificareas depending on the quality and type of glass produced and on thestresses that they must withstand.

In the known art, despite using different materials, a satisfactorybalance between the wear of the various regions of the glass furnace hasnot yet been achieved, and therefore the optimum life of said furnace isstill not achieved due to the early wear of some parts thereof.

In order to reduce the effects of this disparity in wear and ensure themaximum operating life of the furnace, one generally resorts to othersolutions of a mechanical type, such as cooling the structure fromoutside, or to repairs of the most intensely worn regions while thefurnace is hot and running. Known from EP-A-008261 is a refractoryblock, for steel furnaces, having a rectangular cross-section and ametal or graphite insert. The insert has an X-shaped cross-sectionextending along the diagonals of the rectangular cross-section of therefractory block, for facilitating cooling and thereby prolonging theworking life of the block. However, the block is not designed forprolonged contact with molten material and has no means for preventingexcessive wear of the block upon coming into contact with moltenmaterial.

SUMMARY OF THE INVENTION

Accordingly, the aim of the present invention is to provide a compositeand monolithic refractory structure that is shaped like an electro-castrefractory block having various dimensions and chemical-physicalcharacteristics which has, during use, a high resistance tocorrosion/erosion produced by molten baths and particularly by baths ofmolten glass, and therefore a life that is far longer than that normallyachieved with electro-cast materials of any kind and composition.

An object of the invention is to provide a composite refractorystructure conceived and provided so as to be constituted by componentsthat are chemically and/or physically different from each other and arein intimate and continuous contact with each other, one component beingconstituted by refractory material that has been electro-cast or melt orfused with other methods, and one or more parts being constituted by amaterial that is highly resistant to high temperatures and to corrosionand is capable of constituting an effective protective barrier for therefractory component against the continuous attack of a bath of moltenglass or the like.

Another object of the invention is to provide a method for manufacturingsaid composite refractory structure conceived so as to be easy toperform and highly effective without requiring particular and expensiveequipment for performing it.

This aim, these objects, and others which will become apparent from thefollowing description are achieved by a composite and monolithicrefractory structure as defined in the appended claims.

Also according to the invention, a method is provided for the productionof said composite refractory structure as defined in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

Further characteristics and advantages of the present invention willbecome apparent from the following detailed description, given withreference to the accompanying drawings, which are provided only by wayof non-limitative example and wherein:

FIGS. 1,1b and 1a are respectively a perspective view, a front view, anda side view of a type of metallic insert that is shaped like a metalliclamina with an L-shaped profile;

FIGS. 2 and 2a are a side view and a front view of a metallic plate-likeinsert;

FIGS. 3 and 3a are a side view and a front view of another insert shapedlike a metallic lamina;

FIGS. 4 and 4a are a side view and a front view of a laminar insert thatsubstantially has a U-shaped profile;

FIGS. 5, 5b, 5a are respectively a perspective view, a front view, and aside view of another laminar insert folded so as to be L-shaped;

FIG. 6 is a view of an insert constituted by a solid cylindrical bar;

FIGS. 6 bis to 11a are views of a series of elements for supportingand/or suspending an insert (shown in the previous figures) inside amold; said elements can be made of metal, graphite, or refractory orceramic material, or of other adapted materials in various dimensionsand shapes;

FIG. 12 is a median sectional view of a conventional mold for producinga block of electro-cast refractory material, inside which an L-shapedmetallic laminar insert is positioned by using supporting elementschosen among those shown in FIGS. 6 bis to 11a;

FIGS. 12a and 12b are respectively a transverse sectional view of themold, taken along the plane XII--XII of FIG. 12, and a view of FIG. 12taken from "A";

FIG. 13 is instead a schematic view of an example of use of thecomposite structures provided according to the invention, and moreprecisely of a shape of the glass flow region, termed "throat", and ofthe direction (F) of the molten glass flow from the melting tank to theworking end; and

FIG. 14 is a time-based plot of the corrosion of a block and moreprecisely of the progressive corrosion profile compared with the initialprofile of the refractory block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

With reference to the above figures and to the preceding description,the composite refractory structure according to the present invention issubstantially constituted by a monolithic component made of refractorymaterial that is electro-cast (or cast with other methods), is based onceramic oxides, particularly oxides of the AZS system (i.e., oxides ofaluminium, zirconium, silicon), and includes at least one metallicinsert that is fully immersed so as to be concealed, said insert actingas a barrier for protecting the refractory material from the attack ofthe molten glass or similar corrosive product.

Depending on the type of block of electro-cast material and most of allon its relative position in the structure that composes a furnace formolten glass, metal inserts such as for example those shown in FIGS. 1to 6 or any other adapted shape are used, and various kinds of support,such as for example those shown in FIGS. 6 bis to 11a, or similar ones,are used to support said inserts inside a mold for an electro-castblock.

Thus, for example, a first type of insert is constituted by arectangular metallic lamina (FIGS. 1, 1a, 1b) that is folded so as to beL-shaped and have two identical (or optionally different) wings 1a, 1balong a preset radius of curvature R; at the opposite ends, for example,of the wing 1a, there is a recess or notch 2 that is semicircular (orhas another kind of profile) and is meant to interrupt the continuity ofthe insert external perimeter.

Likewise, the metallic insert of FIG. 2 is also constituted by ametallic lamina 2 that is folded so as to be L-shaped and form the twowings 2a and 2b. The wing 2a ends with a part 2c that is folded at anangle and is provided with a semicircular recess 2e. The wing 2b alsoends with a portion that is folded like the portion 2c.

Likewise, the inserts of FIGS. 3, 4, and 5 are constituted by a metallicplate that is folded so as to be L-shaped or U-shaped, are respectivelydesignated by the reference numerals 3, 4, and 5, and are also providedwith a recess 3a, 4a, and 5a.

Only the ends of the insert 4 are not folded.

Said inserts are generally constituted by metals such as Mo, Pt, Ta, W,and the like; they can also be constituted by materials including, forexample, ceramic materials, graphite, carbides, nitrides, borides,suicides, and other similar materials, both as such and as alloys orcompounds and/or composites thereof. They can also be treated by meansof chemical, physical, or mechanical processes to adapt them to theoperating requirements; likewise, their dimensions in length, width, andthickness can vary according to the dimensions of the block for whichsaid inserts must constitute the protective barrier.

The shape of said inserts reproduces the peripheral shape of the part ofthe block that is protected against the attack of the molten glass bath.

Various kinds of supporting elements, such as those shown by way ofexample in FIGS. 6 bis to 11a, are used to stably position the variousinserts inside the mold.

Thus, for example, FIGS. 6 bis and 7 illustrate dowels or pins made ofmetal, graphite, refractory or ceramic materials, or other adaptedmaterial, that can be used to position the insert of FIG. 6, constitutedby a solid cylindrical bar, inside the mold.

The narrower end of the pin of FIG. 6 bis is inserted in the wall of themold, whereas one end of the cylindrical bar-shaped insert of FIG. 6 isarranged in the seat of the protruding part having a larger diameter.The support of FIG. 7 is substantially constituted by a plate 7 made ofmetal or other material which is provided with an adapted hole 7a, inwhich the free end of the cylindrical bar-shaped insert is inserted; thepart 7b shown in dashed lines is instead inserted snugly in the wall ofthe mold. FIGS. 8 to 11a illustrate other supports having a cylindricalor frustum-like shape and provided with laterally formed notches 8b and10b or with recesses 9b and 11b that are formed at their ends. Saidrecesses or notches are meant to snugly accommodate the edge of thewings of the various laminar inserts so as to position them stably.

FIGS. 12, 12a and 12b illustrate a complete example of the positioningof an insert inside a mold which is shaped like a rectangularparallelepiped, shown in FIG. 12, prior to the casting of the moltenrefractory.

The insert arranged therein is of the type of the one designated by thereference numeral 1 in FIG. 1, that is to say, a lamina with an L-shapedprofile and with wings 1a and 1b vertically arranged. The lower edge ofthe wing 1a is accommodated in the recess 9b of two vertical cylindricalsupports 9 (FIG. 9), in which the ends that lie opposite to the oneprovided with the recess are inserted snugly in the back wall of themold 12; the wing 1b is likewise arranged on two identical supports 9which are also snugly inserted in the back wall of the mold, as shown bythe sectional view of FIG. 12a. Said wings 1a and 1b are furthermoreretained at the top of the mold by means of two cylindrical elements 8that are horizontally inserted snugly in the contiguous walls of themold (FIG. 12b).

The arrangement of the wings of the insert 1 is such as to allow saidinsert to remain fully contained inside the mold and thus also insidethe finished refractory block, and is also such as to keep its wingsstably parallel and close to the inside surfaces of the mold walls.

Of course, the other kinds of support can be used to position andsupport the other kinds of insert, such as those shown merely by way ofexample in the accompanying figures.

The method for casting the molten refractory material inside the mold toachieve the composite structure according to the invention thereforeentails the following operating steps:

positioning, supporting, and/or suspending at least one insert insidethe casting mold with the aid of said appropriately structured andconfigured supporting elements, so that said insert is fully immersed inthe part made of electro-cast refractory so that the surfaces that mustconstitute the barrier against the attack of the molten glass bath arelocated at, and proximate to, the surfaces of the block that will beexposed to said attack;

casting the molten refractory material inside the mold with anappropriate method and equipment ensuring control of the flow-rate andof the adequate directionality of the casting flow, in order tointroduce the molten material in the planned time, prevent relativemovements of the insert or inserts with respect to the mold, and thusachieve uniform and complete filling of said mold.

The importance of choosing the materials constituting the elements thatposition and support the insert or inserts, their shape, and theirdimensions, is evident during this step.

The definition of these correlated characteristics must be performed inaccordance with the nature of the insert and of the refractory part andis essential to:

prevent, during casting, the elements from undergoing an alteration ofany nature that might cause a movement of the insert from its originalplanned position;

produce permanent structural continuity between the elements and therefractory part of the composite structure after the block has cooled;and

produce permanent, intimate, and mutual contact without discontinuitiesbetween the elements and the insert at their interface after the blockhas cooled.

It is furthermore necessary to cool the composite structure constitutedby the refractory part and by the insert according to an appropriatethermal cycle, so as to ensure the formation of a uniformmicrocrystalline structure of the refractory part and permanent intimatecontact between said refractory part and the insert.

For this purpose, it is indispensable that the choice of the nature ofthe refractory part, of the insert, and of the supports be such thatthey have a consistent expansion behavior.

The block produced according to the described method can be used forexample for each one of the positions numbered 1 to 9 of FIG. 13. SaidFIG. 13 illustrates one of the possible embodiments of the region of theglass furnace technically termed "throat".

Intense corrosion of the electro-cast refractory material occurs in thisregion and mostly affects the blocks in positions 1, 2, and 3, andparticularly the block in position 1, which is the most criticalelement, also from the point of view of its structural function in thethroat of FIG. 13.

The throat is an essential element of the structure of the furnace, andits wear in practice determines the duty life of said furnace, sometimesentailing an early shutdown. Corrosion of the blocks that constitute thethroat occurs according to the typical profile shown in FIG. 14, where Fdesignates the direction of the flow of molten glass, B designates theprofile of the initial block, and t₁ and t₂ designate the progressivecorrosion profiles in the times t₁ and t₂, where t₂ is subsequent to t₁.

The insert I, shown in dashed lines inside the block in position 1, byinterposing itself between the molten glass bath and the refractorymaterial, acts as a protective barrier for the refractory body,preventing said body from making contact with the molten glass, thusavoiding its corrosion and/or erosion and in practice increasing theworking life of the block.

The invention as described and illustrated according to some preferredembodiments is of course susceptible, in its practical execution, offurther structurally and functionally equivalent modifications andvariations, especially in the molten refractory materials, in theinserts, and in the supports, as well as in the number and relativeposition of said inserts and supports, without abandoning the scope ofthe protection of the invention.

What is claimed is:
 1. Composite and monolithic refractory structure,for making furnaces for glassmaking, comprising:a block-shaped componentmade of AZS electro-cast refractory material, said block-shapedcomponent having at least one molten glass bath contacting externalsurface; at least one protective element embedded inside saidblock-shaped component and resistant to the attack of molten glassbaths, said protective element having substantially a shape of acontinuous plate having a major extending surface which is locatedproximate to, and substantially parallel to, said molten glass bathcontacting external surface of said block-shaped component whereby toconstitute a continuous protective barrier against said attack of moltenglass for the remainder of the AZS electro-cast refractory materiallocated behind said protective layer opposite to said molten glass bathcontacting external surface.
 2. Refractory structure according to claim1, wherein said protective element is made of at least one metal,selected from the group consisting of molybdenum, tantalum, tungsten,and platinum.
 3. Method for producing a monolithic composite refractorystructure, comprising the steps of:preparing a mold for the productionof a block of AZS electro-cast refractory material; preparing at leastone protective insert that is resistant to the attack of molten glassand having substantially a shape of a continuous plate with a majorextending surface; positioning, inside said mold, said protective insertso that said major extending surface of said protective insert islocated proximate to and substantially parallel to a wall portion ofsaid mold; casting molten AZS electro-cast refractory material into saidmold so as to surround said protective insert with said molten AZSelectro-cast refractory material arranged inside said mold between saidmajor extending surface of said protective insert and said wall portionof said mold and behind said protective insert with respect to said wallportion of said mold; and stopping the casting when the mold is filledand then cooling the molten AZS electro-cast refractory material in saidmold surrounding the protective insert so as to form a monolithiccomposite refractory structure having said protective insert embeddedinside solidified AZS electro-cast refractory material and having amolten glass bath contacting external surface formed from the AZSelectro-cast refractory material which was arranged inside said moldbetween said major extending surface of said protective insert and saidwall portion of said mold in said casting step such that said moltenglass bath contacting external surface is located proximate to andsubstantially parallel to said major extending surface of saidprotective insert whereby said protective insert constitutes acontinuous protective barrier against attack of molten glass for theremainder of the AZS electro-cast refractory material located behindsaid protective insert opposite to said molten glass bath contactingexternal surface.
 4. Method according to claim 3, wherein said castingstep comprises casting of refractory material that are meltableelectrically and are selected from the group consisting of Al₂ O₃, SiO₂,ZrO₂, Cr₂ O₃, and MgO.
 5. Method according to claim 4, wherein saidpreparing step comprises preparing said protective insert made of atleast one metal selected from the group consisting of Mo, Pt, Ta, and W.6. Refractory structure according to claim 1 wherein said protectiveelement has at least two wings substantially extending mutuallyperpendicularly.
 7. Refractory structure according to claim 1 whereinsaid protective element has bent and curled edges.
 8. Refractorystructure according to claim 1 wherein said protective element has atleast one edge provided with a recess for engagement with a pin-shapedsupport for facilitating a stable positioning of said protective elementinside a mold for casting AZS electro-cast refractory material forforming said block-shaped component made of AZS electro-cast refractorymaterial and having said protective element embedded therein.
 9. Methodaccording to claim 3 wherein said preparing step comprises preparingsaid protective insert having at least two wings substantially extendingmutually perpendicularly.
 10. Method according to claim 3 wherein saidpreparing step comprises preparing said protective insert having bentand curled edges.
 11. Method according to claim 3 wherein saidpositioning step comprises connecting pin-shaped supports inside saidmold and wherein said preparing step comprises preparing said protectiveinsert having at least one edge provided with a recess for engagementwith said pin-shaped supports for facilitating a stable positioning ofsaid protective insert inside said mold.
 12. Method according to claim11 wherein said position step comprises providing at least some of saidpin-shaped supports with end grooves and positioning said protectiveinsert in said mold such that edges of said protective insert areinserted in said end grooves.
 13. Method according to claim 12, whereinsaid preparing and casting steps comprise selecting materials for saidprotective insert, for said AZS electro-cast refractory material, andfor said supporting elements which have similar thermal expansioncharacteristics.